Apparatus and method for measuring operating temperatures of an electrical component

ABSTRACT

An apparatus and a method for measuring operating temperatures T j  of a component, particularly transient temperatures T j  in the breakdown region of the component  2  during a breakdown operation, are provided. The component temperature T j  at a point of time t i  is ascertainable from a measurement of the breakdown voltage U d  and the breakdown current I of the component  2  at the specific point of time t i  during the breakdown operation using a measuring device, by comparing the measurement data to reference measurement data recorded in advance.

FIELD OF THE INVENTION

[0001] The present invention relates to an apparatus and a method formeasuring operating temperatures of an electrical component, e.g.,transient temperatures of the component during breakdown operation.

BACKGROUND INFORMATION

[0002] In general, in the field of semiconductor technology, theperformance of a component is strongly dependent, inter alia, on thepermissible operating temperatures. A very common reason for componentfailure is temperatures which are too high during operation, whichdamage or even completely destroy the component. Both for the user whodimensions a specific application, and for the semiconductormanufacturer that specifies its product, the knowledge of the componenttemperature that result under specific field conditions is therefore ofgreat interest.

[0003] Thus, the problem of detecting the component temperature,particularly transient changes of temperature in the interior of thecomponent during operation, is important.

[0004] At the moment, the following approach to solving this problem isfound in the prior art. The so-called barrier-layer temperature orjunction temperature T_(j) is determined via the measurement of theforward voltage of p-n junctions of the component. The p-n junctions arejunctions between p-doped and n-doped regions of a semiconductor, andthey are, for example, a component of rectifier and Zener diodes, orexist in the form of the intrinsic body diode of a field-effecttransistor or MOSFET transistor.

[0005] This known approach utilizes the fact that the voltage, whichmust be applied in the forward direction to a p-n junction for aspecific current flow, is a function of the component temperature at thelocation of the p-n junction. Based on the functional correlation of thevoltage, of the current and the component temperature, by measuring theforward voltage with respect to a given forward current, it is possibleto infer the component temperature.

[0006] In the known approach above, the fact that the measurementcurrent must flow in the forward direction across the component turnsout to be disadvantageous, i.e., this method is not usable as long asanother operating state of the component prevents this forward current.Even during such operating states, however, it is often necessary toexactly determine the internal temperature conditions of the component.

[0007] For example, using this known method, it is not possible toexamine the reverse breakdown of a diode, in which a high voltage isapplied in the reverse direction, such that the diode breaks down and ahigh so-called avalanche current flows in the reverse direction. Thehigh fields and currents lead to strong heating of the component, thehottest location in the component being precisely at the p-n junctionwhich is breaking down. However, to determine the temperature prevailingat the p-n junction using the approach described above, it is necessaryto wait until the reverse current has nearly completely decayed, inorder to be able to allow a measurement current to flow in the forwarddirection through the component. This time delay results in aninaccurate measurement, since the temperature now present no longercorresponds to the temperature peak at the p-n junction occurring duringthe breakdown, because in the meantime, the heat has already beendistributed over a larger area of the component or to the thermallycoupled surroundings of the component.

[0008] However, it is precisely the transient temperature peaks whichare critical in damaging the component and which cannot be measuredsufficiently accurately using the above approach according to the priorart.

SUMMARY

[0009] The present invention provides the advantage that the peaktemperatures occurring during critical operating states and theirvariation with time may be exactly detected during breakdown operationof the semiconductor component.

[0010] The present invention utilizes the fact that the breakdownvoltage and the breakdown current of the component are measured at aspecific point of time during the breakdown operation using a measuringdevice, and the component temperature at this point of time isascertained by comparing these measured values to previously recordedreference measurement data of the connection between the breakdownvoltage and the breakdown current.

[0011] Therefore, the barrier-layer temperature may be measured directlyduring the breakdown operation, and its characteristic may be tracked ona time scale during the active component operation. The operation is notimpaired by the detection of the breakdown voltage. Moreover, thetransient internal component temperature is measured, which isrelatively independent of external influences due to the mounting of thecomponent.

[0012] Furthermore, the real-time data of the temperature variation ofthe component with time may be utilized directly for calibratingnumerical model calculations. A subsequent extrapolation of temperaturevalues measured with time delay is therefore no longer necessary.

[0013] Because the temperature measurement is more precise, developersare able to verify and optimize their theory/simulation models andcalibrate certain parameters. The specification of the semiconductorproducts may also be safeguarded or verified by direct transientmeasurement data.

[0014] Finally, the application developers are able to test the load ofthe used components directly in the circuit during the active breakdownoperation. It is thereby possible to better take advantage of theso-called safe operating range of the component for the application,since the limits of permissible thermal operating parameters aredirectly discernible.

[0015] In addition, the method according to the present invention may beused on packaged and unpackaged components, and it may also be used forrepeating switching operations, e.g., for repetitive avalanchebreakdowns, since the method itself takes up no more time than theavalanche-operation itself, i.e., there is no dead time between theindividual measurements, and therefore no additional measuring time forthe component.

[0016] According to one exemplary embodiment of the present invention,the component is designed as a semiconductor component capable ofelectrical breakdown, having at least one p-n junction. For example, thecomponent takes the form of a transistor, e.g., a MOSFET transistor orbipolar transistor, or a diode, e.g., a Zener diode.

[0017] According to another exemplary embodiment of the presentinvention, the component is designed as a component capable of tunnelbreakdown, having an insulating layer, e.g., a gate oxide layer, betweentwo conductor layers.

[0018] In a further exemplary embodiment of the present invention, theelectrical storage device of the apparatus takes the form of aninductor.

[0019] In another exemplary embodiment of the present invention, theswitching device of the apparatus is designed as a MOSFET switch.

[0020] In a further exemplary embodiment of the present invention, thecomponent is designed as a MOSFET transistor that is usable at the sametime as a switching device.

[0021] According to a further exemplary embodiment, the measuring devicefor measuring the breakdown voltage and the breakdown current of thecomponent at a specific point of time during the breakdown operation isdesigned as an oscilloscope.

[0022] According to another exemplary embodiment, the apparatusadditionally has an evaluation unit which, from the measured voltagecharacteristic and current characteristic, automatically ascertains theassociated barrier-layer temperature characteristic of the component.

[0023] In another exemplary embodiment, reference measurement data arerecorded in a steady-state manner as a calibration curve atpredetermined component temperatures, the predetermined componenttemperatures being suitably selected for the relevant component in sucha way that during later breakdown operation, the measured value of thebarrier-layer temperature may be determined with a predeterminedaccuracy.

[0024] In a further exemplary embodiment for the recording of referencemeasurement data, the component is brought homogeneously to apredetermined temperature by a heating/cooling device.

[0025] In one further exemplary embodiment, reference measurement dataare recorded immediately after the electrical breakdown of thecomponent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a circuit diagram of an apparatus for measuringbarrier-layer temperatures T_(j) of a component capable of electricalbreakdown according to an exemplary embodiment of the present invention.

[0027]FIG. 2 is a graphic representation of breakdown characteristiccurves U_(d) v. (I) at different component temperatures T as referencemeasurement data according to an exemplary embodiment of the presentinvention.

[0028]FIG. 3 is a graphic representation of the transient currentcharacteristic and voltage characteristic during the breakdown operationaccording to the exemplary embodiment in FIG. 2.

[0029]FIG. 4 is a graphic representation of the transient characteristicof barrier-layer temperature T_(j) during a breakdown operation of thecomponent according to the exemplary embodiment illustrated inconnection with FIGS. 2 and 3.

DETAILED DESCRIPTION

[0030] In the figures, the same reference numerals denote the same orfunctionally equivalent components. FIG. 1 illustrates a circuit diagramof an apparatus 1 for measuring operating temperatures, particularlybarrier-layer temperatures T_(j) during breakdown operation, of acomponent 2.

[0031] Apparatus 1 may be used for recording reference measurement datafor obtaining calibration curves, with an additional heating/coolingdevice further described below. The reference measurement data areintended to represent the correlation among breakdown voltage U_(d),reverse current I and component temperature T, thus also temperatureT_(j) in the blocking-state region.

[0032] In accordance with this exemplary embodiment of the presentinvention, apparatus 1 according to FIG. 1 is used for measuring thereference measurement data.

[0033] An inductor 3 is charged via a switching device 4, e.g. a MOSFETtransistor 4, for a specific time duration to a specific charge. This isrepresented in FIG. 1 by the square-wave pulse at the gate of MOSFETtransistor 4. MOSFET transistor 4 has a higher breakdown voltage thanthe p-n junction of component 2 to be tested, in order to supply asufficiently large charge for the breakdown of component 2. However, abreakdown voltage of an equal amount is sufficient.

[0034] After MOSFET transistor 4 is switched off, the energy stored ininductor 3 discharges via the p-n junction of component 2 shown inFIG. 1. Consequently, the voltage at the p-n junction of component 2increases until the breakdown takes place and a discharging current I inthe reverse direction, so-called reverse current I, flows off via thediode, i.e. component 2.

[0035] Component 2 heats up due to the Joule heat given off by thecurrent flow. However, reverse current I decays with time, as is shownin FIG. 3. Therefore, different temperature developments come about inthe blocking-state region of component 2 during the breakdowncharacteristic. For recording the reference measurement data, it isnecessary to measure the measured breakdown voltage U_(d) and breakdowncurrent I at component temperatures T which are constant, even in theblocking-state region.

[0036] A homogeneous component temperature T is achieved by heating orcooling the entire component using a heating/cooling plate. However,other methods, e.g. regulating component 2 to the desired temperatureusing a thermoflow, are also conceivable. The heating or cooling processis carried out for a specific period of time until a homogeneoustemperature distribution of component 2 has ensued in such a way thatdesired barrier-layer temperature T_(j) is present particularly in theblocking-state region at the p-n junction of component 2 to be tested.

[0037] To prevent influence of the Joule heat on the homogeneoustemperature distribution in response to a flow of reverse current Iduring the breakdown operation of component 2, breakdown voltage U_(d)and breakdown current I in the reverse direction are measuredimmediately after the breakdown of the p-n junction, i.e. 1 to 2 μsafter the breakdown, for recording the reference measurement data. Thesteep rise of the voltage upon commencement of the breakdown may be usedas the trigger signal for this measurement, the measurement beingcarried out at a specific, sufficiently brief point of time after thetrigger signal.

[0038] Voltage value U_(d) present at this point of time, given flowingreverse current I, yields a reference measuring point of calibrationcurve U_(d) (I) shown in FIG. 2.

[0039] The measurement of the reference measurement data described aboveis repeated for various switch-on times of the gate voltage of MOSFETtransistor 4. With increasing switch-on time, inductor 3 is charged morestrongly, i.e. with a higher energy, by which current I flowing at thebeginning of the breakdown may be adjusted accordingly.

[0040] By such variations of current I at the point of time of thebreakdown, corresponding reference measurement data pairs (U_(d), I) areobtained for each homogeneously set temperature T, thereby yielding, forexample, a set of calibration curves shown in FIG. 2.

[0041] The circuit for determining calibration curves is to bedimensioned in a manner suitable for covering the current rangenecessary for the calibration. In order not to load component 2 toomuch, the discharge duration of inductor 3 may be designed to be asshort as possible, for example, by using as small an inductor 3 aspossible.

[0042] In addition, depending on the component or development stage, itmay be expedient to determine a separate set of calibration curves foreach individual component 2, or to use a single set of calibrationcurves representative of a complete component generation. In the lattercase, it may possibly be sufficient to merely adjust individual smallermanufacturing tolerances by suitable scaling of the present set ofcalibration curves. For example, breakdown voltage U_(d) of specificcomponent 2 may be measured at at least one defined reference point (I,T), and the total set of calibration curves adapted to this referencepoint.

[0043] According to a further exemplary embodiment of the presentinvention, with reference to FIG. 1, it is possible to dispense withswitching device 4, and instead, to use a field-effect transistor as thecomponent 2 that is to be calibrated for charging inductor 3. Accordingto this exemplary embodiment, the intrinsic body diode of field-effecttransistor 2 exists as a p-n junction, and breaks down after the gatevoltage is switched off.

[0044] After the reference-data measurement has concluded, the set ofcalibration curves shown in FIG. 2 is obtained which represents thecorrelation of breakdown voltage U_(d) and breakdown current I in thereverse direction for predetermined component temperatures T orbarrier-layer temperatures T_(j). The spacings of predeterminedtemperatures T or T_(j) are to be dimensioned in such a way, specific tothe component and application, that respective barrier-layer temperatureT_(j) may be read accurately enough for the measurement described below.

[0045]FIG. 3 shows a graphic representation of a measurement ofbreakdown voltage U_(d) and of breakdown current I as a function of timeduring the breakdown operation of component 2 according to an exemplaryembodiment of the present invention.

[0046] Apparatus 1 according to FIG. 1 described above may be used formeasuring barrier-layer temperatures T_(j) during the breakdownoperation of component 2. Only the heating/cooling device for heating orcooling component 2 is to be dispensed with in this case.

[0047] An oscilloscope (not shown) may be used as a measuring device formeasuring breakdown voltage U_(d) and breakdown current I.

[0048] In breakdown operation of component 2, the measuring devicemeasures a value pair (breakdown voltage U_(d), breakdown current I),from which associated barrier-layer temperature value T_(j) may beascertained using the set of calibration curves in FIG. 2.

[0049] In the following, the method described above shall be explainedin greater detail, with the aid of FIGS. 2, 3 and 4, according to anexemplary embodiment of the present invention.

[0050] As shown in FIG. 3, the value pair represented by the two x's ismeasured at a point of time t_(i) of approximately 0.09 ms, withbreakdown voltage U_(d) at point of time t_(i) having a value ofapproximately 97.2 V and breakdown current I at point of time t_(i)having a value of approximately 27.5 A.

[0051] As FIG. 2 shows, by comparing the value pair represented by “x”to the set of calibration curves depicted, especially to the two nearestbreakdown characteristics, one obtains barrier-layer temperature T_(j)existing at point of time t_(i) in the blocking-state region ofcomponent 2 by interpolation of temperatures T of the calibration curvesused.

[0052] Thus, in the present exemplary embodiment, at point of timet_(i), for measured breakdown voltage U_(d) and measured breakdowncurrent I, one obtains a temperature T_(j) of approximately 155° C.prevailing in component 2 in the blocking-state region, as is evident inFIG. 2. The two respective nearest reference measuring points of the twonearest calibration curves are advantageously used for theinterpolation.

[0053] The method described above may be repeated at each point of timet_(i), by which the characteristic curve of barrier-layer temperatureT_(j) shown in FIG. 4 is obtained.

[0054] Although the present invention was described above in light of anexemplary embodiment, the invention is not restricted to it, but can bemodified in diverse ways.

[0055] For example, a suitable software algorithm may be used for anautomatic evaluation of the measurement data and indication ofbarrier-layer temperature T_(j) prevailing at specific point of timet_(i) in component 2.

[0056] The apparatus described above for plotting the set of calibrationcurves, as well as possible avalanche test circuits, may be integratedin a measuring apparatus which then automates the measurement-dataacquisition and evaluation of the calibration curves. For example, arapid processing unit may convert the measured values into a temperaturecurve online, which indicates transient barrier-layer temperature T_(j)to the user in quasi real time during the component operation.

[0057] Since the barrier-layer temperature can only be evaluated duringthe breakdown of the p-n junction of the component, i.e. as long as afinite avalanche current I is flowing in the reverse direction, theforward voltage method known in the art may be used for plotting thefurther progression of the barrier-layer temperature after the avalanchecurrent has decayed. In this manner, the decay of the temperature couldthen, for example, be further tracked on a longer time scale. Thus, itmay possibly be advantageous to combine the known forward-voltage methodand the breakdown-voltage method according to the present invention.

[0058] Moreover, the present invention may be used on all componentshaving p-n-doped semiconductor junctions, e.g., transistors, diodes,etc., as well as on components capable of tunnel breakdown. Suchcomponents capable of tunnel breakdown may, for instance, be made up oftwo conductor layers separated from each other by an insulating layer,e.g., a gate oxide, it being possible for a tunnel breakdown to occur atthe insulated junction between the two conductive layers and theinsulating layer at a specific breakdown voltage.

[0059] Metal semiconductor components (e.g., Schottky diodes) capable ofbreakdown are also measurable using the method of the present invention.

1-21. (canceled).
 22. An apparatus for measuring an operatingtemperature of an electrical component during a breakdown operation,comprising: an electrical storage device connected to the electricalcomponent capable of electrical breakdown; a switching device forcharging the electrical storage device to a selected electrical charge,wherein, after the switching device is switched off, the electricalstorage device discharges via the electrical component to switch theelectrical component into a breakdown operation; and a measuring devicefor measuring a breakdown voltage characteristic and a breakdown currentcharacteristic of the electrical component.
 23. The apparatus accordingto claim 22, wherein the electrical component is a semiconductorcomponent with an electrical breakdown mode, the semiconductor componenthaving at least one p-n junction.
 24. The apparatus according to claim22, wherein the electrical component is a component with a tunnelbreakdown mode, the electrical component having an insulating layerbetween two conductor layers.
 25. The apparatus according to claim 22,wherein the electrical component is one of a MOSFET transistor, abipolar transistor, and a diode.
 26. The apparatus according to claim22, wherein the electrical storage device is an inductor.
 27. Theapparatus according to claim 22, wherein the switching device is aMOSFET switch.
 28. The apparatus according to claim 25, wherein theelectrical component is a MOSFET transistor, wherein the MOSFETtransistor also functions as the switching device.
 29. The apparatusaccording to claim 22, wherein the electrical component is a Schottkydiode.
 30. The apparatus according to claim 22, wherein the measuringdevice is an oscilloscope.
 31. The apparatus according to claim 22,further comprising: an evaluation unit that ascertains temperaturevariation of the electrical component based on the measured voltagecharacteristic and the measured current characteristic.
 32. A method formeasuring an operating temperature of an electrical component during abreakdown operation, comprising: recording reference measurement datafor establishing a correlation between a breakdown voltage and abreakdown current of the electrical component at predetermined componenttemperatures; measuring, using a measuring device, the breakdown voltageand the breakdown current of the electrical component at a selectedpoint of time during the breakdown operation; and ascertaining abarrier-layer temperature at the selected point of time by comparing themeasured breakdown voltage and the measured breakdown current to thereference measurement data.
 33. The method according to claim 32,wherein the reference measurement data are recorded in a steady-statemanner at predetermined component temperatures, the predeterminedcomponent temperatures being selected as a function of the electricalcomponent.
 34. The method according to claim 32, wherein the electricalcomponent is brought to a predetermined temperature level homogeneouslyby a heating/cooling device, for recording of reference measurementdata.
 35. The method according to claim 32, wherein the referencemeasurement data are recorded immediately after the electrical breakdownof the electrical component.
 36. The method according to claim 32,wherein the barrier-layer temperature at the selected point of time isobtained from the reference measurement data by interpolation.
 37. Themethod according to claim 32, wherein the electrical component is asemiconductor component with an electrical breakdown mode, thesemiconductor component having at least one p-n junction.
 38. The methodaccording to claim 32, wherein the electrical component is a componentwith a tunnel breakdown mode, the electrical component having aninsulating layer between two conductor layers.
 39. The method accordingto claim 32, wherein the electrical component is a Schottky diode. 40.The method according to claim 32, wherein the electrical component isone of a MOSFET transistor, a bipolar transistor, and a diode.
 41. Themethod according to claim 32, wherein the measuring device is anoscilloscope.
 42. The method according to claim 32, wherein anevaluation unit is additionally provided to ascertain, from the measuredvoltage characteristic and the measured current characteristic, theassociated temperature variation of the electrical component.